This invention relates to the utilization of liquid fuel oils, particularly Fuel Oil No. 2 through Fuel Oil No. 4, as an alternate source of fuel in normally gas fired equipment, such as boilers, gas turbines, various industrial furnaces and particularly for hydrocarbon steam reformers. With increasing demands placed upon natural gas reserves by use of natural gas in the production of petrochemicals and petrochemical products, a scarcity of natural gas has been created such that it is necessary to find sources of alternate fuels for gas fired equipment. Of course, it is possible to remove burners designed for natural gas service and replace them with burners designed for burning fuel oil but such is not always economic or advantageous to the operation of equipment where natural gas may be intermittently available for use as a fuel. This is particularly true with respect to hydrocarbon steam reforming furnaces, as described, for example, in U.S. Pat. Nos. 3,257,172; 3,672,847 and 3,768,980, where many such burners are in operation and a conversion to fuel oil service would require days of down time with great loss of productivity.
While it has previously been disclosed, in U.S. Pat. No. 3,393,964 for example, to atomize liquid hydrocarbons in the burner itself with a normally gaseous fuel, such operation would require the replacement of all existing natural gas burners with a specialized burner and, therefore, is impractical. U.S. Pat. No. 3,291,191 describes the broad concept of vaporizing a normally liquid fuel to make it interchangeable with natural gas in the operation of a natural gas burner. It has previously been known to vaporize liquid fuel by heating. Such heating, however, results in heavy residue and consequent formation of coke requiring frequent shut downs for cleaning, and thus is generally unacceptable.
Other methods have been described wherein a portion of the fuel oil is burned with the gaseous products used to vaporize additional fuel oil for burning in a gas fired burner, as described in U.S. Pat. No. 1,987,401. U.S. Pat. No. 3,480,416 describes a method of preparing a gaseous fuel by cracking a portion of a liquid fuel and conjointly heating water to form a gas stream for further use either as a feed for flame cracking or for fuel. Again, there are many consequent disadvantages to such a method. Also, previously, naphthas and light petroleum distillates have been vaporized to replace natural gas as fuel but the prior art does not describe such a system for use of such heavier fuel oils.
U.S. Pat. No. 4,089,805 describes a method for vaporizing 25 to 75 percent by weight of a liquid fuel oil thereby producing a gasiform hydrocarbon fuel and a liquid residue, separating the gasiform hydrocarbon from the liquid residue, superheating the gasiform fuel and burning the gasiform fuel in a gasiform burner.
According to the present invention, it is an object to provide a system whereby fuel oil, such as No. 2 through No. 4 and equivalent, can be essentially fully vaporized (e.g. 99+ percent) to form a gaseous product suitable for use interchangeably, and intermittently, with natural gas in a burner designed for natural gas combustion. It is also an object of this invention to provide apparatus and a method whereby fuel oils, such as Fuel Oil No. 2 through Fuel Oil No. 4 can be used as an alternate fuel for gas without significant coking in the furnace or equipment utilized for vaporizing the oil.